1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image, and to an image forming method using the toner.
2. Discussion of the Background
The electrophotographic image forming methods are broadly classified to dry developing methods and wet developing methods. The dry developing methods are further classified to one-component and two-component developing methods. A toner used in any methods needs to be positively or negatively charged, according to the polarity of an electrostatic latent image. A charge controlling agent is most effectively added to the toner to maintain a charge of the toner.
A variety of charge controlling agents are available, and chrome-containing complex compounds have conventionally been used because of being inexpensive and negatively charging. Japanese published unexamined application No. 2000-321819 discloses a toner including a chrome-containing complex compound and a polyester resin having an acid value of from 15 to 30 mg KOH/g. Although this improves an edge of negative chargeability, the developer initially has no problem but noticeably deteriorates in its chargeability as time passes in an environment of high humidity because the polyester resin varies due to environment.
Japanese published unexamined application No. 2003-255617 discloses a charge controlling agent having a specific X-ray diffraction pattern, with which a developer does not deteriorate in its chargeability in an environment of high humidity. In addition, even when a carrier is charged low, the developer has high transferability, producing images having good granularity without producing foggy images. However, toner are having smaller particle diameters to improve image quality and toners having a particle diameter 7.0 μm need further charging buildability. When a charge controlling agent is included in a toner too much to increase charging buildability, the toner has higher elasticity because the charge controlling agent works as a filler, resulting in deterioration of low-temperature fixability of the toner. Japanese published unexamined application No. 2002-53539 discloses a toner including a charge controlling agent which is a mono azo gold-bearing compound having a purity not less than 90%. The toner has high negative chargeability but the durability thereof is unknown at all. Above all, when a toner has a small particle diameter, the toner recycled is an ultra fine powder, resulting in noticeable poor charging buildability thereof.
Because of these reasons, a need exists for a toner having high colorability and maintaining low-temperature fixability without producing foggy images even after used or stored at high temperature for long periods.